Cable television (CATV) systems typically include transmission equipment, such as headend equipment that receives satellite signals and demodulates the signals to baseband. The baseband signal is then converted to a radio frequency (RF) signal or optical signal for transmission from the headend to receiving equipment, such as a set top box. The set top box couples to the subscriber's equipment, such as, for instance, a television set.
Cable television taps are situated along the CATV distribution system to split the signals off to the receiving equipment. Taps serve to enable subscriber output ports to provide a signal to a subscriber. Taps usually include an incoming port for receiving RF signals from the headend and outgoing ports for splitting off portions of the RF signal to the set top box. Algorithms for decoding and processing commands in certain set top boxes requires a delay time between commands to ensure complete command decoding and processing. Thus, set top and other addressable devices were designed to handle one command at a time.
Conventional addressable taps normally include a microprocessor and input and output ports. The microprocessor interprets the commands from the headend and provides the signal to the designated addressed subscriber output port. Each output port corresponds to a subscriber signal drop location. Normally, a tap contains 2, 4, or 8 subscriber output ports, thereby serving 2, 4 or 8 subscribers. A properly operating tap is necessary for a subscriber to receive cable television service. Numerous factors can cause a tap to malfunction. For instance, because the tap has only a single microprocessor, it can become overloaded by a continuous flow of commands and consequently drop commands, thereby causing subscribers to incorrectly receive or not receive service.
Further, taps can be damaged by environmental factors. For example, strong winds, lightening, or power surges can cause the tap to malfunction, which requires resetting the tap. Resetting the tap can occur remotely from commands sent from the headend. U.S. patent application Ser. No. 09/401,477 filed Sep. 22, 1999, entitled “Method and Apparatus for Restoring Port Status in a Cable Television Tap,” assigned to Scientific-Atlanta discloses mechanisms for periodically refreshing ports of a tap to correct inadvertent status changes and is incorporated by reference in its entirety herein. Although refreshing the port status allows the outgoing ports of the tap to maintain proper status, if a command from the headend is being processed when a refresh command is sent, the in process command may be dropped.
Therefore a need exists for an addressable tap that utilizes the existing microprocessor, transmission protocols and receiving equipment in a cable television system and can process a continuous stream of addressable commands.